1. Field of the Invention
This invention relates to a valve device and more particularly to a temperature responsive valve device which provides an on-off control of fluid communication in response to change in temperature.
2. Description of the Prior Art
Various emission control systems have been proposed such as a secondary air supply system where CO, HC and the like, which are contained within imperfect combustion gases from vehicle engines, are reacted within an exhaust system of a vehicle. In such secondary air supply system, it is desired that supply of air is allowed only under the prescribed running conditions of the vehicle in view of the drivability of the vehicle. Thus, conventionally, valve devices have been proposed which provide on-off control of secondary air supply passages in response to signal vacuum within an intake manifold of a vehicle engine.
Furthermore, it is desired that the supply of secondary air be controlled in response to changes in temperature, whereby temperature responsive valve devices have been proposed which control on-off transmission of the signal vacuum. Such temperature responsive valve devices have valve portions which are adapted to selectively transmit one of the intake manifold's vacuum and atmosphere to a signal chamber of the secondary air supply valve device. Thus, within the temperature responsive valve device, a first filter is arranged near an inlet port which receives the intake manifold vacuum and a second filter is arranged near an inlet port which communicates with atmosphere.
Furthermore, it is desired that the temperature responsive valve devices have a delay means of an orifice type between the first filter and the outlet port to thereby delay transmission of intake manifold vacuum pressure. In order to prevent clogging of the associated orifice by foreign matter, a third filter has to be provided between the orifice and the secondary air supply valve device. This results in high cost and complex constructions of the temperature responsive valve devices.